JP4969775B2 - Optical device package having reflector and alignment post - Google Patents

Description

  Semiconductor optoelectronic devices such as laser diodes for optical transceivers can be efficiently fabricated using wafer processing techniques. In general, in the wafer processing technology, a large number (for example, several thousand) devices are simultaneously formed on a wafer. The wafer is then cut into separate individual chips. While it is possible to reduce the cost per chip by simultaneously producing a large number of chips, each chip is generally packaged and / or assembled into a single system that protects the chip and It must provide both electrical and optical interfaces for using devices on the chip.

  Assembling packages or systems that include optoelectronic devices is often costly. This is because a large number of optical elements must be aligned with the semiconductor device. For example, the transmit side of an optical transceiver chip may include a Fabry-Perot laser that emits an optical signal from the edge of the chip. However, the desired optical signal path may require light to emerge from another direction (light from, for example, the surface of the package). The optical signal can be deflected from the original direction to a desired direction by the reflecting mirror. In addition, a lens or other optical element may be required to collect or modify the optical signal and improve the coupling between the optical signal and an external optical fiber. The alignment of the reflector with respect to the chip edge, the alignment of the lens with respect to the reflector, and the alignment of the optical fiber with respect to the lens can be a time / expensive process.

  Wafer level packaging is a promising technique for reducing the size and cost of packaging of optoelectronic devices. In wafer level packaging, components that were conventionally formed and bonded separately are fabricated on a single wafer corresponding to multiple packages. The resulting structure can be glued individually or simultaneously and later cut into separate individual packages.

  There is a need for packaging techniques and structures that can reduce the size and / or cost of optoelectronic assemblies.

  According to one aspect of the present invention, a reflector and a side-emitting laser are attached to the submount. The submount includes active or passive electrical components that are electrically connected to the laser. The submount can further include an optical element, and the reflector is disposed at a position where the optical signal from the laser is reflected through the submount. The alignment post can then be mounted on the submount at the position where the optical signal comes out. Align the two by inserting a post into one end of the sleeve and a ferrule containing the optical fiber into the opposite end of the sleeve, thereby efficiently coupling the optical signal to the optical fiber. be able to.

  The laser can be protected by a transparent encapsulant deposited on the submount and surrounding the laser. Alternatively, the cap can be secured to the submount to form a cavity that houses the laser, and the reflector can be configured in the cap as a reflector for the cavity wall.

  One particular embodiment of the present invention is a device that includes a submount, an edge emitting laser, and a reflector. The submount includes a conductive trace, and the edge emitting laser is electrically coupled to the conductive trace. The reflector is disposed at a position where an optical signal from the edge-emitting laser is reflected through the submount. An alignment post can be attached to the submount at a position where an optical signal is emitted. Furthermore, an optical element such as a diffractive lens can be mounted in the path of the optical signal or integrated with the submount along the path of the optical signal.

  In one variation of this embodiment, the reflector is a reflective portion of the inner wall of the cap that is attached to the submount and seals the laser into the cavity. Alternatively, a transparent encapsulant such as silicone can be applied to the submount to contain and protect the laser.

  The same reference numbers used in different drawings indicate similar or identical components.

  According to one aspect of the invention, an edge emitting laser package includes a submount and a reflector for directing an optical signal from the laser through the submount. The submount can be a semiconductor substrate including passive circuit elements or active circuit elements attached to a die. An alignment post can be attached to the submount at a position where the optical signal emerges after reflection from the reflector. The reflector can be a separate element or it can be part of a cap that is attached to the submount to seal the laser in the cavity. If the reflector is a separate element, a transparent encapsulant material can be applied to the laser and submount to protect the laser.

  In the wafer level fabrication process for these packages, multiple lasers are attached to a single submount wafer. The reflector is attached to the submount wafer at a position where the optical signal from each laser is reflected. The reflector can be a separate element or it can be a reflective part of the cavity in the cap wafer. The dice are protected from the environment by encapsulating material applied to accommodate the laser or by a sealed cavity formed by attaching a cap wafer to the submount wafer. The submount wafer is cut and separated into individual packages. Alignment posts can be attached to the submount before or after package separation to simplify alignment of the package in the optical subassembly (OSA).

  FIG. 1 illustrates a structure 100 created during a wafer level packaging process, according to one embodiment of the invention. The structure 100 includes a number of edge emitting lasers 110. The laser 110 can be of conventional design and can be made using techniques well known in the art. In one specific embodiment, each laser 110 is a Fabry-Perot laser used in the transmitter portion of the optical transmitter.

  Each laser 110 is in one of the cavities 140 formed between the submount wafer 120 and the cap wafer 130. In the embodiment of FIG. 1, the laser 110 is bonded and electrically connected to the submount wafer 120. Laser 110 can be glued or otherwise bonded to the desired location using conventional die bonding equipment. In structure 100, bonding pads 115 on laser 110 are connected to internal bonding pads 122 on wafer 120 by wire bonding.

  The wafer 120 is mainly made of silicon and / or other materials that transmit the wavelength of the optical signal from the laser 110 (for example, 1100 nm or more). The wafer 120 also includes circuit elements such as bond pads 122 and electrical traces or vias (not shown) that connect the laser 110 to external terminals 124. In the illustrated embodiment, the external terminals 124 are on the top surface of the submount wafer 120, but alternatively, the external terminals can be disposed on the bottom surface. In addition, active devices (not shown) such as transistors, amplifiers, or monitors / sensors can be incorporated into the wafer 120.

  Cap wafer 130 is fabricated to include a recess or cavity 140 in a region corresponding to laser 110 on submount wafer 120 and a cutting channel 144 in a region on external terminal 124. The wafer 130 can be made of silicon or any convenient material suitable for forming the desired shaped cavity 140. Cavity 140 can be formed in a variety of ways, including but not limited to molding and casting, ultrasonic machining, (isotropic, anisotropic, or plasma) etching. Is not to be done.

  All or part of the surface of the cap wafer 130, including the cavity 140, is reflective so that the reflector 150 is integrated into the cap wafer 130 at the location required to reflect the optical signal from the laser 110 in the desired direction. Or coated with a reflective material. In an exemplary embodiment, a reflective metal is deposited to form reflector 150, but the metal is limited to a predetermined area to prevent wicking when soldering wafers 120, 130 with solder. be able to. The reflector 150 can simply be planar to reflect or bend the optical signal in the desired direction, or alternatively can be non-planar to provide beam shaping if desired. Can be.

  In the exemplary embodiment, cap wafer 130 is silicon, and anisotropic etching of silicon forms cavities 140 having very smooth and flat facets on the <111> plane of the silicon crystal structure. The reflector 150 is a facet coated with a reflective material such as a Ti / Pt / Au metal stack. The preferred angle of the reflector 150 relative to the surface of the wafer 130 is 45 so that the optical signal emitted by the laser 110 parallel to the surface of the wafer 120 is reflected in a direction perpendicular to the surface of the submount wafer 120. °. Using silicon wafers cut off axis by 9.74 °, a 45 ° angle can be obtained for each reflector 150. However, etched silicon cut on-axis or off-axis at different angles can also produce an angled reflector 150 suitable for many applications.

  Optionally, an optical element 160, such as a lens or prism, can be bonded or integrated to the submount wafer 120 along the path of the optical signal from the laser 110. In FIG. 1, optical element 160 is a lens that is integrated into wafer 120 and serves to collect the optical signal to better couple the optical signal to optical fibers and other optical devices not shown in FIG. is there. US patent application Ser. No. 10 / 210,598 entitled “Optical Fiber Coupler with Relaxed Alignment Tolerance” is a bifocal diffractive lens suitable for optical element 160 where it is desirable to couple an optical signal into an optical fiber. Is disclosed.

  The submount wafer 120 and the cap wafer 130 are aligned and joined to each other. The wafers 120 and 130 can be bonded using various wafer bonding techniques including soldering, thermal compression bonding, and bonding agent bonding, but the bonding technique is not limited thereto. In an exemplary embodiment of the invention, the wafers 120, 130 are joined together by a gold / tin eutectic solder and the cavity 140 is sealed. Sealing the cavity 140 protects the enclosed laser 110 from environmental damage.

  After the wafers 120, 130 are bonded, the structure 100 can be cut to create individual packages, each containing a laser 110 sealed within a cavity 140. In particular, the cutting channel 144 allows the cap wafer 130 to be cut along the line 136 without damaging the underlying structure such as the external terminals 124. After cutting the cap wafer 130, the submount wafer 120 can be cut along line 126 into separate individual packages.

  FIG. 2 illustrates a structure 200 according to an alternative embodiment of the present invention that uses a flip chip structure to bond a laser 210 to a submount wafer 220. In flip chip packaging, the bond pads 212 of the laser 210 are placed in contact with the conductive pillars or bumps 222 on the submount wafer 220. The bumps 222 typically include solder that can be reflowed to physically and electrically bond the laser 210 to the wafer 220. An underfill (not shown) can also be used to enhance the mechanical integrity between the laser 210 and the submount wafer 220. Structure 200 is substantially the same as structure 100 described above, except for the method of bonding laser 210 to wafer 220 and electrically connecting it.

  1 and 2 illustrate the structure formed during the wafer level packaging process, the same applies to a single edge emitting laser in which the reflector redirects the direction of the optical signal from the laser through the submount. Technology can be used.

  FIG. 3A shows a cross-sectional view of a submount 300 for an optical device package according to an exemplary embodiment of the present invention. In the wafer level packaging process, the submount 300 becomes part of the submount wafer and is separated from other similar submounts only after the submount wafer is bonded as described above. Alternatively, when making a single package, the submount 300 can be separated from other similar submounts before the optical device laser is bonded to the submount 300.

  The submount 300 can be fabricated using the wafer processing technique described in the US patent application entitled “Integration of Optical Elements and Electronics” of the applicant's representative serial number 10030566-1. In the illustrated embodiment, the submount 300 includes a silicon substrate 310 that is transparent to optical signals using long wavelength light.

  On the silicon substrate 310, a lens 320 is formed, for example, by alternately stacking polysilicon and oxide layers to create a diffractive or refractive lens of the desired shape or characteristics. Applicant's US Patent Application entitled “Method of Making a Diffractive Optical Element” with Attorney Docket No. 10030769-1 describes several processes suitable for making lens 320.

  A flat insulating layer 330 is formed on the silicon substrate 310 to protect the lens 320 and provide a flat surface on which the metallization can be patterned. In the exemplary embodiment of the present invention, the insulating layer 330 is a TEOS (tetraethylorthosilicate) layer that is approximately 10,000 mm thick.

  The conductive trace 340 can be patterned from a metal layer, such as a 10,000 W thick TiW / AlCu / TiW stack. In the exemplary embodiment, trace 340 is formed by a process that includes depositing metal onto layer 330 and a stripping process that removes undesirable metal. An insulating layer 332 (eg, another TEOS layer about 10000 mm thick) is deposited to fill and insulate the trace 340. The insulating layer can include an opening 338 that is optionally covered with Au (not shown) so that it can be electrically connected using wire bonding. In this way, any number of embedded trace layers can be constructed. It is possible to form a passivation layer 334 of a relatively hard and chemically resistant material, such as a silicon nitride layer of about 4500 mm thickness, on top of another insulating layer to protect the underlying structure . A metal layer 360 (eg, a Ti / Pt / Au stack about 5000 mm thick) is formed on the passivation layer 334 to bond / solder the cap.

  The submount in the above package can incorporate passive or active circuitry. FIG. 3B shows the layout of a submount 350 that includes a substrate 310 with active circuitry 370 fabricated in and on top. The active circuit 370 can be used to process input or output signals from one or more chips that are to be bonded to the submount 350. The substrate 310 is a semiconductor substrate on which an active circuit 370 incorporated using standard IC processing technology can be fabricated. Once the circuit 370 is made, internal pads or terminals 342 for connection to the optoelectronic device die and external bond pads or terminals 344 for connection to the outside are formed, connected to each other and / or active circuit. Connected to 370. In the embodiment shown in FIG. 3B, the external pad 344 is for I / O signals such as power, ground, and data signals.

  The optical element 320 is in an area without electrical traces or components on the substrate 310 and adapts to the optical signal reflection path.

  A solder ring 360 that joins the cap is formed between the active circuit 370 and the external bond pad 344. A separate cap sized to access the external bond pad 344 can be joined to the solder ring 360. Alternatively, in a wafer level packaging process where multiple caps are fabricated in a cap wafer, the cap wafer can be partially etched to accommodate the external pad 344 before bonding the cap wafer to the submount wafer. Is possible.

  FIG. 4A is a perspective view of a cap 400 suitable for attachment to the submount 300 of FIG. 3A. The cap 400 can be made using standard wafer processing techniques. In an exemplary embodiment of the invention, anisotropic etching of the silicon substrate 410 forms cavities 420 with very smooth facets 430 on the <111> plane of the silicon crystal structure. At least the target facet 430 of the cavity 420 is reflective or coated with a reflective material (eg, a Ti / Pt / Au metal stack). Thereby, the facet 430 of the cap 400 can function as a reflector.

  FIG. 4B shows a perspective view of a cap 450 according to an alternative embodiment of the present invention. The cap 450 includes a structure 460 that includes two layers including a stand-off ring 462 and a backing plate 464. The advantage of the cap 450 is that the two layers 462,464 can be treated differently and / or made from different materials. In particular, the standoff ring 462 can be made of silicon that has been completely etched and formed with a ring having a flat mirror surface 430 at the desired angle, and the backing plate 464 can be glass or the like that transmits light of shorter wavelengths. Can be made of any material.

  To assemble an optical device package using the submount 300 and the cap 400 or 450, a laser is placed on the submount 300 using a conventional die attach and wire bonding process or alternatively a flip chip packaging process. Install. Electrical connection to the trace 340 on the submount 300 can provide power to the laser and carry data signals to and from the chip. The cap 400 or 450 is attached to the submount 300 after the laser is attached. This can be done at the single package level, as described above, or at the wafer level. Sealed by patterning AuSn (or other solder) on submount 300 or cap 400 so that when the wafers are brought together, the solder reflow process creates a seal that protects the encapsulated laser. Can be obtained.

  FIG. 5 illustrates an optical subassembly or package 500 according to one embodiment of the invention. Package 500 includes an edge-emitting laser 510. The laser 510 is mounted on and electrically connected to the submount 520 and is sealed in a cavity 540 that is sealed when the cap 530 is bonded to the submount 520. Cavity 540 shows a structure in which cap 530 is made of silicon having a <100> plane at an angle of 9.74 ° from the main bottom and top surfaces. The face of the reflector 550 is formed along the <111> face of the silicon substrate, and therefore the cap 530 can be wet etched so that it is at a 45 ° angle with the main face of the cap 530 and the submount 520.

  According to one embodiment of the present invention, the monitor chip 515 is mounted on the submount 520 and electrically connected. The monitor chip 515 includes a photodiode that measures the intensity of the optical signal from the laser 510. Thereby, the laser in the laser 510 can be monitored and a constant output can be maintained.

  Post 560 is aligned with the optical signal emitted from tip 510 after reflection from reflector 550. In particular, the post 560 can be epoxy bonded to the submount 520 where the light beam exits. The post 560 can take many shapes, including but not limited to a hollow cylinder or substantial structure, such as a light transmissive cylinder or sphere. The post 560 performs an alignment function in which the optical fiber in the connector is aligned with the light emitted from the laser in the package 500.

  FIG. 6 illustrates an optical subassembly or package 600 according to an alternative embodiment of the present invention. Package 600 includes chips 510 and 515 that connect to submount 520 as described above. The package 600 has a reflector 630 that reflects the optical signal from the laser 510 through the submount 520 instead of a cap having an integrated reflector. The reflector 630 can be made of glass, silicon, or any other suitable material that can be formed and coated to provide a reflective facet having a desired orientation. The post 560 is attached to the submount 520 at a position where the optical signal exits from the submount 520.

  Encapsulant material 640, such as silicone or other suitable material that transmits the optical signal, surrounds and protects dies 510,515. FIG. 6 shows the encapsulant material 640 surrounding the chips 510, 515 and the reflector. However, the size and shape of the encapsulant 640 can vary. In general, the encapsulant 640 should sufficiently cover the chips 510, 515 and fill the space between the laser 510 and the reflector 630 to minimize optical signal degradation. Conventional techniques such as degassing and careful application of the encapsulant material 640 can be used to avoid optical signal degradation during transmission through the encapsulant material 640.

  FIG. 7 shows an optical assembly 700 that includes the subassembly 500 of FIG. The optical assembly including the subassembly 600 can be similarly configured. The assembly 700 includes a sleeve 720 that includes a post 560 of the package 500 and an optical fiber 730 in a ferrule 740. Ferrule 740 can be part of a conventional optical fiber connector (not shown). The sleeve 720 is basically a hollow cylinder having a bore that receives both the post 560 and the ferrule 740. Thus, the inner diameter of one end of the sleeve 720 is sized to accept a standard optical fiber ferrule and can be any size, but is typically 1.25 mm or 2.5 mm in diameter. In the case of a uniform bore as shown in sleeve 720 in FIG. 7, post 560 has a diameter that matches the diameter of ferrule 740. Alternatively, the bore diameter of the sleeve 720 can be different at each end to accommodate the post 560 and ferrule 740, respectively. In yet another alternative embodiment, the function of the sleeve 720 and the ferrule 740 is such that an optical fiber (e.g., typical about 125 [mu] m) aligned with an opening that houses a post 560 (e.g., having a diameter of about 1 mm or greater) Can be incorporated into a single structure (including a bare diameter).

  The top surface of post 560 serves as a fiber stop and controls the “z” position of ferrule 740 relative to laser 510, and thus the “z” position of optical fiber 730. Thus, the length of post 560 is selected to efficiently couple the optical signal from package 500 into post 560 that abuts the optical fiber. In particular, the length of the post 560 depends on any light collecting element that can be formed in or on the submount 520.

  Engagement of post 560 and ferrule 740 within sleeve 720 determines the position of post 560 and optical fiber 730 in the “x-y” plane. In this way, the optical fiber 730 is positioned in the center in the xy plane with respect to the post 560, and the light emitted from the laser 510 is placed in the center of the optical fiber 730. Thus, proper placement of the post 560 having the desired length during fabrication of the subassembly 500 simplifies the alignment of the optical fiber 730 for efficiently coupling optical signals.

  The external terminal package 500 or 600 generally connects to a circuit board that includes other components such as an optical transmitter or optical transceiver. FIG. 8 illustrates one embodiment of the present invention in which the terminals on the top surface of the package connect to the flexible circuit 810. The flexible circuit 810 is generally a flexible tape or substrate that includes conductive traces that can be soldered to external terminals of the package 500 or 600. Holes can be created through the flexible circuit 810 to accommodate protruding structures such as the cap 530 or encapsulant 640 of the package 500 or 600. A rigid circuit board 820 to which other components 830 of the optical transmitter or transceiver are attached electrically connects to the optoelectronic device of the package 500 or 600 via the flexible circuit 810 and the submount in the package. . In an alternative embodiment of the present invention, the external terminals of the package 500 or 600 are directly connected to the rigid circuit board if the resulting sleeve 720 orientation is convenient for the fiber optic connector. Can do.

  Although the invention has been described with reference to particular embodiments, the description is only an example of the invention's application and should not be taken as a limitation on the invention. Various adaptations and combinations of the features of the embodiments disclosed herein are also included within the scope of the invention as defined by the claims.

1 is a cross-sectional view of a portion of a structure formed during a wafer level packaging process of a semiconductor optical device according to an embodiment of the present invention that uses wire bonding for electrical connection. FIG. 1 is a cross-sectional view of a portion of a structure formed during a wafer level packaging process of a semiconductor optical device according to one embodiment of the present invention that uses a flip chip structure for electrical connection. FIG. 1 is a cross-sectional view of a submount of an optoelectronic device according to an embodiment of the present invention. 1 is a plan view of a submount according to an embodiment of the present invention that includes active circuitry within the submount. FIG. FIG. 6 is a perspective view of a cap of a semiconductor optical device package according to an alternative embodiment of the present invention. FIG. 6 is a perspective view of a cap of a semiconductor optical device package according to an alternative embodiment of the present invention. FIG. 6 illustrates an optical device package according to an embodiment of the present invention including a cap and an optical alignment post. FIG. 6 illustrates an optical device package according to an embodiment of the present invention that uses an encapsulant and an optical alignment post. It is a figure which shows the optical device package of FIG. 5 at the time of attaching a sleeve and an optical fiber connector. FIG. 3 illustrates an embodiment of the present invention in which an optical assembly connects to a rigid circuit board via a flexible circuit board.

Explanation of symbols

100 structure
110 Edge-emitting laser
115 Bonding pads
120 Submount wafer
122 Internal bonding pad
124 External terminal
130 Cap wafer
140 cavity
144 cutting channel
150 reflector
160 Optical elements
200 structure
210 laser
212 bond pads
220 Submount wafer
222 Conductive bump
300 submount
310 Silicon substrate
320 lenses
330 Insulation layer
338 opening
340 conductive trace
334 Passivation layer
342 Internal pad
344 External bond pad
350 submount
360 metal layer
400 cap
410 Silicon substrate
420 cavities
430 facet
450 cap
460 structure
462 Stand-off ring
464 Backing plate
500 optical package
510 Edge-emitting laser
515 monitor chip
520 submount
530 cap
540 cavity
550 reflector
560 alignment post
600 optical package
630 reflector
640 capsule material
700 light assembly
720 sleeve
730 optical fiber
740 Ferrule
810 Flexible circuit
830 Other components

Claims (9)

A submount including conductive traces;
A die having a laser (510) electrically coupled to the conductive trace in the submount (520);
A reflector (550) arranged to reflect an optical signal from the laser (510);
An alignment post (560) made of a light transmitting material attached to the submount (520) at a position where it exits from the submount (520) after the optical signal from the laser (510) is reflected by the reflector (550). And a registration post (560) that aligns the optical signal to the center of the optical fiber and efficiently couples the optical signal to the optical fiber. Wherein the reflector (550), formed of a part of the inner wall of the cap (530), wherein mounted on the submount (520) sealing the laser (510) into the cavity (540), The device of claim 1 .   The device of claim 1, further comprising a transparent encapsulant (640) attached to the submount (520) and containing the laser (510).   The device of any one of claims 1 to 3, further comprising an optical element (320) integrated within the submount (520) along the path of the optical signal. Electrically connecting the die with the laser (510) to the submount (520);
A reflector (550) is attached to the submount (520) at a position where an optical signal from the laser (510) is reflected,
The optical signal from the laser (510) is reflected by the reflector (550) and then exits from the submount (520), and the optical signal is aligned with the center of the optical fiber on the submount (520). And attaching an alignment post (560) made of a light transmissive material that efficiently couples the optical signal to the optical fiber.
A process that includes each step.   The process of claim 5, further comprising encapsulating the laser (510) in a transparent material (640) that protects the laser (510).   The step of attaching the reflector (550) includes attaching a cap (530) to the submount (520) to seal the laser (510) in a cavity (540), the reflector (550) comprising the The process of claim 5, wherein the process is integrated into the wall of the cavity (540).   The process of any one of claims 5 to 7, further comprising disposing an integrated optical element (320) in the submount (520) along the path of the optical signal. Electrically connecting the laser comprises connecting a plurality of lasers (110) to a submount wafer (120) including a plurality of submounts, respectively.
The process further includes
Cutting the submount wafer (120) to separate the submount to which the laser (110) is attached from another submount to which another laser (110) is attached,
9. A process according to any one of claims 5 to 8.

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